Add regression test for issue #756.

(cherry picked from commit 899d459233)

ivtest/ivltests/br_gh756.v

@@ -0,0 +1,15 @@
+module dut(input [3:0] x);
+
+initial begin
+  $display("%b", x);
+  if (x === 4'b1111)
+    $display("PASSED");
+  else
+    $display("FAILED");
+end
+
+endmodule
+
+module test;
+  dut dut('1);
+endmodule

ivtest/regress-sv.list

@@ -205,6 +205,7 @@ br_gh553		normal,-g2009		ivltests
 br_gh556		normal,-g2009		ivltests
 br_gh568		normal,-g2009		ivltests
 br_gh672		normal,-g2009		ivltests
+br_gh756		normal,-g2009		ivltests
 br_ml20171017		normal,-g2009		ivltests
 br_ml20180227		CE,-g2009		ivltests
 br_ml20180309a		normal,-g2009		ivltests